Conventional wheelchairs have push handrims fixed to the drive wheels. A user propels the wheelchair by grasping the handrims and then exerting a forward stroke. The drive wheels move forward concurrently with the forward thrust made by the user.
Typically, the handrim is attached to the drive wheel either by being bolted or welded to the rim of the wheel. Another manner of attachment is by fixing the handrim to the wheel using the wheel spokes. The diameter of the handrim also determines the amount of leverage the handrim provides the user to engage when propelling the wheelchair. The amount of leverage is determined by the distance the handrim is from the center of rotation. The fact that the handrims are statically fixed to the wheel, however, limits the amount of leverage possible to that of the diameter of the wheel.
Another disadvantage associated with conventional wheelchairs is that they can be quite difficult to maneuver in certain situations. For instance, the most problematic situation is where the user has to confront a steep incline or under other circumstances where forward momentum is lost quickly. Because forward progress requires the user to release the handrim to reach back for another forward stroke, there is a tendency for wasted movement due to the fact that the most direct route between the end of a forward stroke and the beginning of a next forward stroke often is not taken. When a user releases the rim to reach back for another forward stroke, he or she must expend an amount of energy to simply regrasp the handrim. The amount of energy expended regrasping the handrim increases with the steepness of the incline. Such conventional handrim systems are thus quite difficult and often frustrating to use.
Still another disadvantage of conventional wheelchairs is that the wheelchair handrims are often difficult to master for wheelchair users who are physically weak or have little or no experience using wheelchairs. This is because such users expend significant energy concentrating on simply maintaining a grasp of the handrim to facilitate their forward progress. Such handrims are also less satisfactory for sport wheelchairs that are used in racing or the like. Moreover, standard wheelchair handrims do not permit the user to selectively engage an amount of leverage which is appropriate for the terrain being covered.
There has therefore been a long-felt need to overcome these and other problems associated with conventional wheelchairs and wheelchair handrims.